Row 1: Single crochet in 2nd chain from hook and in each chain across - 11 stitches.
Row 2: Chain 1, turn.
Working through back loops only, single crochet in each stitch across.
Repeat Row 2 until piece measures about 9 1/2 in. (24 cm), when slightly stretched.
Sew short sides of Cozy together for about 1/2 in. (1.5 cm) at top and at bottom, leaving remaining 2 1/2 in. (6.5 cm) open for mug handle.
With sewing needle and thread, sew button, centered, onto one edge of handle opening. Use spaces between stitches as buttonhole.